What is Single source of truth?
A single source of truth is not a piece of software, it is a decision, and one decision per kind of data. The CRM leads for customers, the calendar for appointments, accounting for invoices. Everything else is a copy. The common misreading is to take the principle as one system for everything: what is meant is not a single tool but an unambiguous place per thing.
Without that decision, every automatic connection has to guess. When two systems disagree, in practice the record written last wins, not the correct one. An address maintained in the newsletter tool then overwrites the address corrected during a sales call. The mistake does not show up at the moment of writing, it shows up weeks later at send time.
In practice a table with four columns is enough: kind of data, leading system, who may change it, what happens on a conflict. For a small business that is rarely more than six rows. That list is the precondition for an integration doing anything more than pushing data back and forth.
Why does Single source of truth matter?
According to Eurostat, 25.4 per cent of Austrian firms with 10 to 49 employees use CRM software at all (2025 survey). For three in four small firms the leading place for customer data is therefore not a system but a mailbox, a spreadsheet or somebody's head. The single source of truth question does not start at integration time, it starts considerably earlier.
Single source of truth in practice
- 01A customer's phone number is valid as it stands in the CRM; the newsletter tool receives it and may not write it back.
- 02The quotation amount is valid from the quotation document, the task list merely displays it.
- 03An appointment is valid from the calendar; the note in the customer file is a copy and gets overwritten on a conflict.
From the journal
- Address, opening hours, phone number: your website is the refereeGoogle and Apple change your opening hours when users report something and check the change against public sources, first of all your website. When your core details read differently in different places, it is not your profile that decides but what your own site says. How often customers run into wrong details, how a change gets into your profile, which places really count, what happens with holidays, a move or a new number, and how to set one source everyone believes.
- Connecting tools: when an integration is enough and when it hides the problemConnecting two tools is an afternoon's work these days. Whether it helps is decided before that: an integration moves data, it does not make decisions. If the rule about who does what and when is missing, the connection only speeds up the confusion. Here is how to tell the two cases apart in five minutes.
